1. Understanding of Squeeze Casting Technology
As a process technology, squeeze casting has been widely used in production, but many problems have been exposed in practical application. For example, the quality of castings is not stable, the yield is not high enough, there are inclusions, porosity, local porosity and other defects, resulting in unstable mechanical properties. These problems are not only related to the equipment, but also to the selected squeeze casting process. As a process technology, it has its specific application scope and characteristics. The applicator must comprehensively consider the specific structure and requirements of parts (such as shape, size, performance and batch) to determine the best process plan. Do not regard the process as a universal technology, and choose blindly without knowing its characteristics, which is easy to cause failure.
In the research and application of squeeze casting technology, the researchers should not regard the plastic deformation structure of the casting as a major indicator of the success of the squeeze casting. The high demand for this index will inevitably limit the application scope of this process in actual production. Those who only produce castings with very simple shape cannot occupy more shares in the fierce market competition.
At present, the classification methods of squeeze casting are disordered, which often lead to conceptual misunderstanding in practical application. The author thinks that the classification method of squeeze casting should be determined according to the stress form of the casting and the state of the liquid metal filling cavity [26]. According to this point of view, squeeze casting can be divided into two categories, one is direct squeeze casting (cavity pressurization), which is characterized by the pressure of the punch directly acting on the end and inner surface of the casting, good pressurization effect, and the casting can produce micro plastic deformation structure locally. This process is suitable for producing castings with thick walls and less complicated shapes. The other is indirect squeeze casting (pressing in the pressing chamber). Its main feature is that the pressure on the workpiece during forming is transferred from the liquid metal in the pressing chamber to the casting through the sprue under the action of the pressing (punching) head force. The external force does not directly act on the workpiece, and it has no plastic deformation structure. This method is more flexible and applicable. It can produce castings with more complex shapes and larger wall thickness difference. The castings have high dimensional accuracy and good performance.
2. Status of squeeze casting equipment
The advanced level of domestic squeeze casting equipment is only equal to that of foreign countries in 1970s. The equipment problem has seriously restricted the development of squeeze casting technology in China. At present, the main equipment used in squeeze casting is four column universal hydraulic press. According to the use, there are two situations: one is that the press has not been changed to maintain the original mechanism performance; the other is that the press has been partially modified to add side oil cylinder for core pulling or opening closing type, and some have opened two process holes on the movable crossbeam of the press to install the unloading device of the mold. Obviously, no matter that situation can not meet the requirements of squeeze casting process. The author thinks that it is necessary to develop the full-automatic squeeze casting equipment with supercharging cylinder, double injection punch and side cylinder, with automatic pouring, automatic spraying, automatic picking and trimming, so as to meet the needs of the increasing development of squeeze casting technology.
3. Die material problems of ferrous squeeze casting
It has become a key problem to be solved urgently for the die of ferrous extrusion casting. From the perspective of squeeze casting theory and technology, the squeeze casting of ferrous metal is no longer a problem. Only because the die life is too short, the application of this technology in ferrous metal is limited in a certain sense. High alloy materials of tungsten and molybdenum are used abroad to make die life close to 10000 times. Therefore, if we can solve the problem of die material life of squeeze casting ferrous metal, it will greatly promote the application of squeeze casting technology in ferrous metal and expand the application field of the technology.
4. Design of squeeze casting die
As an important equipment of squeeze casting process, mold has been paid more attention in recent years. Mold design in actual production, especially indirect squeeze casting mold design, is quite different from metal mold, die-casting mold, low-pressure casting mold, forging mold and hot extrusion mold design [25]. It not only requires the mold designer to understand the general knowledge of mold design, but also needs to be proficient in the squeeze casting process, so that the designed mold structure can meet the requirements of the squeeze casting process. Due to the lack of understanding of squeeze casting technology by some mold designers, the unreasonable structure of the designed mold leads to the failure of the whole process test. Finally, the failure is attributed to the failure of the process itself, which has a negative impact on the promotion and application of squeeze casting technology.